This invention relates to an image signal processor, and more particularly to an architecture of an image signal processor in which local image processing such as spatial convolution, non-linear neighbor arithmetic operations can be conducted at high speed and also, expansion of local image area and parallel processing by use of multi-processor can be readily conducted.
Generally speaking, image processing includes the following five steps which are sequentially conducted. That is, (i) observation, (ii) sampling/quantizing/coding, (iii) preprocessing, (iv) feature extraction, (v) object recognition. An object is observed by, generally, a video camera, whose image output is then digitized. In this case, the digitized image includes random noise due to camera characteristics and light reflection. Therefore, preprocessing is used to remove the unwanted noise component. After this processing, features are extracted from the preprocessed image signal and, thereafter, the extracted features are used to identify the object which was observed by a video camera.
In such image processing, the preprocessing consume the most time since it handles huge digital data which represents an image. Current Von Newman type computers are not good at such processing.
Then, several trials have been conducted to realize high-speed image signal processing by parallel-processing image signal data, but it is extremely difficult to parallel-processing whole data of a picture frame. Local parallel image processing, which handles local image data of m-by-n picture elements (pixels) of a picture frame, is applicable to wider processing such as averaging, differential operation, data transformation and so on, and size of circuitry therefor is relatively small. Therefore, development of LSI for use in such local parallel image processing is actively conducted.
A conventional local parallel processing type image signal processor has specific structure which is exclusively used for each image processing function and therefore, in general, does not have general purpose-use-structure and expansion function.
Generally speaking, a local image signal processor is one which picks up local image area data of certain proper size out of input image data, and which makes calculation to such local image area data. That is, a local image signal processor handles image processing of whole picture frame by scanning a window which simply covers a local image area over whole area of a picture frame.
Among image signal processings, there are many processings which are conducted by local processing such as averaging, differential operation, feature extraction and so on. These processings have different complexities one another according to configuration and size of local image area. Generally, such image processing is conducted to local area of approximately 3-by-3 through 16-by-16 pixels.
On example of conventional local image signal processor is disclosed in "Image signal processor computes fast enough for gray-scale video", Tadashi Fukushima, Electronic Design, Oct. 4, 1984, pages 209 through 215. The image signal processor disclosed in Electronic Design has specific exclusive use structure, but does not have general purpose use structure, and further, requires many peripheral/additional circuits to realize expansion processing.